Anomalies of the overall shape of the eye often cause appreciable visual disorders, such as hyperopia, myopia, and astigmatism. The surgical treatment of these and other disorders often involve creating a separation or pocket between the stromal layers of the cornea. Various materials, substances, or inserts may be placed within the pocket to effectuate changes in the geometry of the cornea or deliver drugs or other biologic agents.
For example, these disorders may be corrected using surgical methods involving the implantation of polymeric rings (intrastromal corneal rings) in the eye's corneal stroma to change the curvature of the cornea. Previous work involving the implantation of polymethylmethacrylate rings, allograft corneal tissue, and hydrogels is well documented. One of the ring devices involves a split ring design which is inserted into a pocket in the form of an annular channel dissected in the stromal layer of the cornea. See, for instance, the use of intrastromal rings in U.S. Pat. Nos. 4,452,235 to Reynolds; 4,671,276 to Reynolds; 4,766,895 to Reynolds; and 4,961,744 to Kilmer et al. Temirov et al., "Refractive circular tunnel keroplasty in the correction of high myopia", Vestnik Oftalmologii Mar. 21-31, 1991 suggests the use of collagen thread as intrastromal corneal ring material.
It is also known to use arcuate channels containing a gel-based insert centered on the cornea to correct certain visual disorders. U.S. Pat. Nos. 5,090,955 and 5,372,580, to Simon, suggest introducing a settable polymer or gel into an intrastromal channel and allowing the polymer to set.
These types of procedures typically involve making a partial depth incision into the cornea, either radial or circumferential, and then separating the lamella at a known depth. The separation may be continued or furthered, using a variety of instruments as necessary, until the desired channel or pocket is formed at the desired depth below the surface of the cornea. In U.S. Pat. No. 5,547,468 to Simon et al., for example, once the incision has been formed, a blunt spatula is inserted through the incision to separate the lamella. Following this initial separation of lamella with the blunt spatula, a channel starting instrument is inserted into the incision and then rotated in a manner such that the lamella is separated along an arcuate path.
Creation of the initial separation using an ordinary blunt spatula is often very difficult. There is little visual access to the tip of the instrument at the base of the incision and it may be difficult for the surgeon to feel the bottom of the incision. Improper placement or inadequate manipulation of the instrument by the surgeon may result in an initial separation at the wrong depth relative to the surface of the cornea or no separation at all. Excessive manipulation of the spatula in attempting to initiate the separation at the base of the incision may result in damage or trauma to the incised tissue as well as the tissue below the incision.
There is a need therefor for a pocketing tool constructed to provide a reliable lamella separation at the desired depth below the surface of the cornea which is less sensitive to manipulation difficulties inherent in prior art instruments.